The present invention relates to a multi-layer structure for controlling the transmission of laser radiation, and more specifically to a multi-layer structure whose intermediate layer absorbs the energy from incident laser radiation to decompose and diffract the laser beam to effect significant attenuation thereof. This invention may be used in such structures as aircraft canopies and windshields, helmets and glasses.
In recent years there has been considerable interest in, and a growing development of, lasers whose output optical radiation is of a high intensity. By optical radiation as used herein is meant any portion of the electromagnetic spectrum between about 0.4 and about 15.0 micrometers, and is not confined to the visible portion of the spectrum. Already, considerable effort has been directed toward the development of communication systems utilizing lasers while further technical development is being directed toward the use of a laser as a weapon against aircraft.
Many recent optical devices are fabricated with glass, glass laminates, plastics and plastic laminates to achieve various effects under sunlight or artificial light conditions. Several of these devices have been designed with the idea that light will be diminished as it passes through the device. Many modern applications require these devices to transmit light in the visible portion of the spectrum but diminish light from high intensity laser radiation.
To date, laser weapons have two practical threat wavelengths:
1) approximately 10 micrometers (infrared); and, PA1 2) the range 3 to 5 micrometers. PA1 a) Aerodynamic compatibility with the shape factor of the aircraft; PA1 b) Structural soundness under prescribed aerodynamic environments; PA1 c) Good visibility (transparency in the visible portion of the spectrum); and PA1 d) Ease of fabrication. PA1 e) be capable of withstanding laser radiation for a sufficient time (e.g. t&gt;1 second) to enable the pilot to assume a change in aircraft attitude; PA1 f) be aerodynamically sound to enable the pilot to carry out his assigned mission and/or return to his home base after having been exposed to some maximum level of radiation; PA1 g) to reduce the on-axis level of radiation transmitted, thereby lowering the level of exposure to the pilot.
Depending upon the material exposed to the incident laser beam, the energy from each of these threat wavelengths will either be absorbed by or transmitted through the layer of material in the structure. In general, however, plastics will be absorbing to the 10 micrometer laser while some will transmit in the 3-5 micrometer range. Thus, based upon intelligence reports, different structures and/or materials will be employed according to which laser wavelength is anticipated.
One light disruptive device is disclosed in the patent to Horton, U.S. Pat. No. 3,561,842. The structure relies on the heating effect of absorbed high-intensity optical radiation to destroy a film of light transmissive material which is bonded to a roughened substrate. When high intensity optical radiation impinges the film surface, the energy is absorbed and the film is destroyed, exposing the roughened substrate which deflects the beam. The roughened substrate is a source of possible shortcomings in that it presents additional fabrication steps, difficulties in providing a continuous index of refraction and increased energy absorption of radiation due to the roughened surface. In addition the roughened substrate is a pre-induced damage control device whereas the present invention concerns a self-induced damage mechanism.
Aircraft canopies and windscreens have generally been designed for aerodynamic and economic reasons rather than for laser weapon protection. They are constructed to incorporate the following characteristics:
However, in view of the developments in laser technology it is now desirable that aircraft canopies and windscreens also: